A positive electrode for a nonaqueous electrolyte battery is produced by a method which includes producing a positive electrode paste in which a positive active material, a conductive agent and a binder are dispersed in a solvent, successively coating a current collector made of aluminum foil or the like with the positive electrode paste, and allowing the resultant to pass through a drying furnace so as to volatilize and remove the solvent. When a line speed of a step of coating an electrode plate is increased, a time during which the electrode plate retains in the drying furnace is shortened, thereby causing a shortage of drying.
In order to avoid this, a method of increasing a temperature or an air volume in the drying furnace to increase the drying speed is considered, but the following problem is caused: rapid drying may deteriorate the adhesiveness of a positive composite layer, or may make the concentration of a flammable gas in the drying furnace too high when an organic solvent is used.
Alternatively, a method for securing the retention time in the drying furnace by expanding the drying furnace is considered, but the following problem is caused: higher plant and equipment investment is required.
Examples of a method other than the above methods include a method of increasing a mass ratio of a solid in a positive electrode paste (hereinafter, referred to as “paste solid content”), that is, reducing the content of the solvent, thereby shortening the drying time. However, in this case, the viscosity of the paste is increased, and thus there is the following problem: coatability is deteriorated, for example, fading occurs.
Patent Document 1 discloses that a monomer is chemically bound to the surface of a conductive agent and then polymerized by heating, and the resultant is used for a positive electrode paste, thereby enabling to improve the dispersibility of the positive electrode paste and reduce the viscosity of the positive electrode paste. However, for chemically binding a polymer to the surface of a conductive agent, in general, a process of several stages of chemical reactions needs to be carried out with respect to a conductive agent, which includes fine particles and is difficult to be handled, so that the process may be complicated and production cost may be increased.
Patent Document 2 discloses that a surfactant can be added to thereby improve the dispersibility of a conductive agent in a positive electrode paste. However, it is essential to add and stir a dispersant before the conductive agent is loaded, and thus, a plurality of times of mixing operations are carried out and a reduction in production efficiency may be caused.
Patent Document 3 describes use of a dispersant in order to improve the fluidity of a positive electrode paste including a conductive agent having a large specific surface area in a large amount. However, no comparative data clarifying the viscosity reducing effect by this has been shown. Furthermore, only one dispersant is used herein, and therefore it is not clear whether or not the viscosity reducing effect can be obtained in all dispersants.